Hydrogenation process in presence of a high boiling diluent

ABSTRACT

A PROCESS FOR THE SELECTIVE HYDROGENATION OF DIOLEFINS OVER MONOOLEFINS IN AN AROMATIC DISTILLATE STREAM IN THE PRESENCE OF A NOBLE METAL CATALYST AT A TEMPERATURE BELOW ABOUT 350 TO 400*F. AT WHICH TEMPERATURE SAID AROMATIC DISTILLATE IS AT LEAST PARTIALLY IN THE LIQUID PHASE, IN THE PRESENCE OF A DILUENT HYDROCARBON HAVING A BOILING RANGE ABOVE SAID AROMATIC DISTILLATE WHICH INCREASES THE PROPORTION OF SAID AROMATIC DISTILLATE IN THE LIQUID PHASE AND THEREBY BOTH INHIBITS SOLID POLYMER FORMATION IN SAID PROCESS AND PROVIDES IMPROVED TEMPERATURE CONTROL.

April 4, 1972 R D, CHRlSTMAN EVAL 3,654,132

HYDROGENATION PROCESS IN PRESENCE 0F A HIGH BOILING DILUENT Filed DSC. 1.9, 1969 2 SheetS-Sheut l N www April 4, 1972 R. D. CHRISTMAN ETAL HYDROGENATION PROCESS IN PRESENCE OF A HIGH BOILING DILUENT 2 Sheets-Shoot 2 Filed DeC. 1.9 1969 ,l 3,654,132 HYDROGENATION PROCESS 1N PRESENCE 0F A HIGH BOILING DILUENT Robert D. Christmann, Penn Hills, and `Ioel D. McKinney, Indiana Township, Allegheny County, Pa., assgnors to Gulf Research& Development Company, Pittsburgh, Pa. z

Filed Dec. 19, 1969, Ser. No. 886,554 v Int.,Cl..C10g 23/04 UQS. Cl. 208,-'.-57 9 Claims E. 'ABSTRACT oF THE DISCLOSURE A process for the selective hydrogenation of diolefns over monoolens'in an aromatic distillate stream in the presence of a noble metal catalyst'at a temperature below about350 to 400 F. at which temperature said aromatic distillate is at least partially in the liquid phase, in the presence of a diluent hydrocarbon having a boiling range above said aromatic distillate which increases the proportion of said'aromatic Vdistillate in the liquid phase and thereby both inhibits-'solid polymer formation in said process andprovides improved temperature control.

,I This invention relates to the hydrotreating of pyrolysis gasoline, and more particularly, to the selective hydroge'nationv of diolens contained in the by-product pyrolysis gasolines obtained from the produtcion of ethylene by the pyrolysis of ethane, propane, butane and/ or naphtha range hydrocarbons. Y

Duringthe production of ethylene by the pyrolysis of hydrocarbons, there is produced in addition to the desired oleins, Va considerable quantity of a by-product boiling in the gasoline range (herein referred to as pyrolysis gasoline or aromatic distillate). fPyrolysis .gasoline contains considerable amounts of diolens, such as butadiene, isoprene and cyclo-pentadiene, formed by condensation of ethylene, kas will as residual amounts of olefins, such as pentene, hexene, heptene` and styrene. The pyrolysis gasolinealso contains large quantities of aromatic compounds, such as benzene, toluene, ethylbenzene and xylenes. Such aromatic compounds are of value if recovered in high purity. The aromatic compounds are formed by condensation inring structure of a number of moles of ethylene product. p l

`The presence of yconsiderable amounts of dioleiins and styrenes in' the A,pyrolysis gasoline is undesirable, 'since such diolens andpstyrenes areunstable and tend to polymerize to higher molecular weight compounds. The tendency of the diollens to polymerize is particularly inliuenc'edV by air and light. Gummy materials, which are formed, tend to 'deposit on feed. lines, carburetors, valves and the like, when a pyrolysis gosoline, containing dioletins and styrenes, is blended with other gasolines and subsequently utilized as fuel in interal combustion engines.

In order to use pyrolysis gasolines in gasoline blending., it, is necessary to eliminate substantially all of the diolelin's andfstyryenes, and this can be accomplished by hydrogenating the'styrenes to the corresponding aromatics', and the conjugateddiolens to the corresponding monooelns. In fact, for gasoline blending purposes, it is not desirable to hydrogenate the diolens completely to form saturated hydrocarbons,since saturated hydrocarbons of the paratn type usually have` lower octane ratings than the corresponding monooletins.

l As hereinbefore mentioned, a pyrolysis gasoline aromatic distillate alsocontain's valuable aromatic compounds if the same can be recovered in high purity. The presence of Iminor quantities ot oleiinsin the pyrolysis gasolines United States Patent O 3,654,132 Patented Apr. 4, 1972 ICC hinders the effective separation of such aromatic compounds from the pyrolysis gasoline by known recovery processes. Consequently, in this instance, it is desirable to hydrogenate the olefius completely to form saturated hydrocarbons thereby permitting the recovery of aromatics in high purity from the pyrolysis gasoline by known recovery processes.

The processes available for hydro-treating of pyrolysis gasolines may be classified into two groups. The first group of processes uses a Group VI-Group VIII type catalyst, and operates at temperatures in the range of 400 F. to more than 650 F. As a result of the high operating temperatures, the feed, prior to hydrotreating, must be preheated to 400 F. or higher, and thus there is a great tendency for the formation of gummy materials in the reactor preheat exchangers and/ or furnaces.

The 'second group of processes utilizes a noble metal catalyst and generally operates at temperatures below about 250 or 300 F. At such temperatures, the feed is in the liquid phase and need not be preheated to any high temperature, and the tendency for the dioletins to polymerize is `greatly minimized.

In accordance with the invention, a pyrolysis gasoline, obtained from a plant preparing oletins by the pyrolysis of a hydrocarbon is exotherrnically hydrotreated in the liquid phase with a noble metal catalyst to selectively hydrogenate the diolen's and styrenes contained in the pyrolysis gasoline. The reactor is operated at a temperature of from about to 400 F. and a pressure of from 800 to 1000 p.s.i.g. or more, depending upon the feed stock, its sulfur content and the hydrogen gas purity (i.e., methane content).

Styrene compounds represent the highest boiling fraction of the aromatic distillate feed. Since these compounds are prime gum-formers and since they are not of especially high value in their hydrogenated form, they are advantageously removed from the aromatic distillate before it is fed to the noble metal reactor, so that the noble metal reactor is utilized particularly for the hydrogenation of dioletins. Therefore, the feed to the noble metal reactor can comprise approximately C4 or C5 to 350 or 400 F. naphtha which is free of styrenes.

The noble metal aromatic distillate hydrogenation reactor is operated at a relatively low temperature at which most or a significant proportion of the hydrocarbon feed is in the liquid state. Since at least the highest boiling fraction of the hydrocarbon feed remains in the liquid state, in order to enhance .the amount of liquid in the noble metal hydrogenation reactor in the prior art the highest boiling naphtha fraction has been separated from the product and recycled to the noble metal reactor. As long as the temperature in the noble metal reactor is maintained below the boiling point of this high boiling recycle naphtha fraction a liquid phase is maintained in the reactor.

It was not previously believed that any inert liquid material boiling higher than the aromatic distillate feed should be added to the reactor because such material would dilute the reactants, coat the catalyst surface and slow down the rate of the reaction. However, this attitude of the prior art was based on the belief that all reactions occurring in the reactor are rst order reactions and thereforeequally aiected by a diluent.

It is to be noted that reaction rates in the hydrogenation type of system of this invention are generally first order reactions, i.e. non-exponentially affected by reactant concentration. For example, the hydrogenation reaction itself is a iirst order reaction. However, we now observe that the solid polymer formation reaction is a high order reaction; i.e. exponentially aiected by reactant concentray' tion. The recognition that solid formation in the hydrogenation system is a high order reaction is an important feature of the present invention. It shows that the reaction inhibiting effect of any diluent is much greater upon the polymerization reaction than upon the hydrogenation reaction. It means that the catalyst cycle duration is extremely sensitive to solid polymer precursor concentration and is the reason that while in many operating cycles a long duration is achieved, in others a slight concentration change in the system results in sufficient gum lay-down on the catalyst to severely restrict the length of the run.

We have now discovered that an unexpected advantage in the operation of a noble metal aromatic distillate hydrogenation reactor is achieved when the liquid phase in the noble metal reactor is maintained by introducing an extraneous and substantially inert hydrocarbon fluid to the reactor whose boiling range point is higher than the boiling range of the aromatic distillate feed. Preferably, the entire or most of the boiling range of the diluent is above the upper limit of the boiling range of the aromatic distillate feed. Also, the entire boiling range of the hydrocarbon diluent can be above the highest operating ternperature in the reactor. For example, if the noble metal reactor operates at a maximum temperature of 350 to 375 F., the extraneous fluid is advantageously a furnace oil boiling in the range of about 400 to 650 F.

The discovery of the present invention is illustrated in FIG. 1 which indicates the percentage of liquid feed vaporized at various temperatures with various types and proportions of inert diluents in an aromatic distillate hydrogenation system utilizing a palladium catalyst. Curve A shows the mole percent of liquid feed vaporized at various temperatures when one mole of the highest boiling naphtha product is recycled for each four moles of aromatic distillate feed While curve B shows the effect When two moles of the highest boiling naphtha product are recycled for every four moles of aromatic distillate feed. Curve C shows the effect when the recycle naphtha diluent is replaced with 40G-650 F. furnace diluent oil supplied from an external source in the ratio 1 mole of furnace oil for every four moles of aromatic distillate feed While curve D shows the effect when two moles of furnace oil are utilized for every four moles of aromatic distillate feed. The amount of hydrogen present during the tests of FIG. 1 was two moles per mole of fresh aromatic distillate. The pressure was 700 p.s.i.g. The aromatic distillate used in the tests was a C4 to 300 F. stream.

The unexpected effect according to the present invention is illustrated by comparing curves A and C. Curve A shows that when 1 mole of the recycle naphtha diluent of the prior art is employed per 4 moles of aromatic feed, the system is completely vaporized at 360 F. Since 20 mole percent of the system of curve A comprises recycle naphtha it would be expected that if that 20 percent is replaced With 40G-650 F. furnace oil, at a system temperature of 360 F. the 80 percent of thesystem that was not replaced will still be vaporized but the 20 percent that was replaced by higher boiling material will not be vaporized, i.e. we will be at point -E in FIG. l. Unexpectedly, curve C shows that when only the 20 percent of the system of curve A that Was recycle naphtha is replaced with furnace oil we are at point E at a system temperature of 360 F., indicating that only 49 percent of the system vaporizes rather than the 80 percent that would be expected to vaporize according to the experience of curve A.

The unexpected effect according to the present invention is further illustrated by comparing curves B and D. Curve B shows that when 2 moles of the recycle naphtha of the prior art per four moles of feed is employed, the system is completely vaporized at 370 F. Since 33 mole percent of the system of curve B comprises recycle naphtha it would be expected that if that 33 percent is replaced with 40G-650 F. furnace oil that 67 percent of the system that was not replaced will still be vaporized at a system temperature of 370 F while the 33 percent that was replaced by higher boiling material will not be vaporized,

i.e. We will be at point F in FIG. 1. Unexpectedly, curve D shows that when only the 33 percent of the prior art system of curve B is replaced by furnace oil, we are at point F at a system temperature of 370 F. indicating that only 35 percent of the system vaporizes rather than the 67 percent that would be expected to vaporize according to the experience of curve B. A

The above-observed unexpectedly magnified liquifaction effect at a given temperature when substituting volume for volume a furance oil diluent (B.P. 400to 650 F.) for recycle naphtha (B.P. less than 300 F.) has a potential effect much greater than merely Washing already formed solid contaminants from the catalyst surface. By far the most deleterious catalyst contaminant is solid polymer formed in situ and it is shown below that the liquifaction effect demonstrated above serves to arrest polymerization `before it proceeds to an extent thatl solids are produced.

Any solid polymer formation in the reactor must proceed through initial stages wherein monomers dimerize and trimerize, but most dimers and trimers formed are liquids, not having achieved a sufficiently high molecular Weight to be solid. These liquid dimers and trimers represent about 5 percent of the naphtha feed. However, the dimers and trimers, because they are liquids, can relatively easily further polymerize to the solid state. While it is very difficult to polymerize gaseous precursors to solid polymers, the polymerization of liquid percursors to solid polymers proceeds much more easilyThe rate of such polymerization is proportional tothe 2.5 power of the concentration of the dimer and trimer liquid precursors in their liquid environment, as expressed vin the equation r=k(c)25, where c is the molar concentration' of the liquid precursors of the solid polymers in the liquid phase of the system. Therefore, any increase in liquifaction in the system tends to diminish the concentration of liquid dimer and trimer precursors of solid polymers in the liquid system, thereby reducing the term c in the above question and exponentially reducing the rate of solid polymer formation.

The liquid dimers and trimers which are diluted by the introduction of a furnace oil or other liquid diluent in accordance with this invention generally themselves have :boiling points in the boiling range of the furnace oil or other diluent. In an advantageous embodiment of the present invention, the entire effluent from the low temperature noble metal hydrogenation reactor, because it is substantially free of diolefins, can be safely heated and charged to a relatively high temperature Group VI-'Group VIII metal hydrogenation reactor, such as NiCoMore-V actor, operated at a temperature sufficiently high'to hydrogenate monoolefins but not high enough to saturate a'ro-v matics. In the high temperature reactor, most of or at least a substantial portion of the furnace oil or--other diluent is vaporized, including any dimers and trimers formed in the low temperature reactor-In the vapor phase it is extremely difficult for solidpolymer formation to result and therefore any dimers and trimers present are much more likely to become saturated, thereby rendering them incapable of further polymerization. Since these dimers and trimers are in the furnace oil vboiling range. they now comprise inert diluent suitable for recycle for use as a diluent in the low temperature reactor. Therefore, in each pass through the low and high temperature -reactors the amount of furnace oil boiling" range material increases in accordance with this invention. By'actual'ob'- servation, the amount of such increase is about 2 percent per pass. 1s j ..1

Advantageously, the total polymer arresting effect of this invention is a pyramiding of two separate effects. First, the dilution effect upon rate of solid polymerformation, according to the equation r=k(c) 25,' is exponential.

That is, the reduction in rate of solid polymer formation from liquid precursors is realized exponentially by Vincreasing the amount of diluent liquid for the liquid polymer precursors. Secondly, it is shown in FIG. 1 that the substitution of furnace oil or similar diluent for the recycle naphtha diluent utilized in accordance with the prior 'art has much more than a volume-for-volume effect upon the total amount of the liquid in the system. An unexpectedly great effect upon liquication in the system is achieved by substitution of furance oil for recycle naphtha in accordance with the present invention and this unexpectedly great liquication has an exponential effect upon rate of solid-former formation in the system.

The present invention is directed particularly to a hydrogenation process utilizing a noble metal catalyst whose actors'utilizing a noble ymetal catalyst are conventionally low temperature. Temperatures within hydrogenation reactors utilizing a noble metal catalyst are conventioinally sufficiently low that the feed hydrocarbon is not entirely vaporized. Therefore, in these reactors the prior art only utilizedre'cycle of the higher boiling product fraction to insure a sucient quantity of 'liquid in the system and it was not heretofore deemed necessary to add an extraneous liquid as a diluentl to such low temperature reactors. However, it is precisely because the temperature in these reactors is low that solid polymer precursors cannot vaporiz`e,but remain inthe liquid` state. While solid polymer precursors'in the liquid state can be relatively easily further polymer'ized Vto solid polymers, formation of solid polymers from the same precursors would be nearly impossible if these materials werev vaporized. Therefore, it is. the veryfactthat the noble metal reactor is operated at a low temperature whereat the system tends to maintain a liquid phase that imparts high significance to the enhanced dilution of dimer and trimer material resulting from the magnifiedy liquifaction effect of this invention. 7 A-hydrocarbon` material whose boiling point or boiling range is .above the boiling range of the aromatic distillate feed can be employed as a diluent. If a high temperature hydrogenator is utilized downstream from the noble metal hydrogenator, the diluent preferably has a boiling point or boiling range so that it remains at least a partially liquid in the second hydrogenator in order to wash from thefsurface of the catalyst of the second hydrogenation any solid polymers formed therein. The molar ratio of diluent boiling above the aromatic distillate range to aromatic ,distillate in the feed to the noble metal reactor can vary within wide limits. For example, the ratio can be u0.1 to 2;, generally, land 0.1 to 0.7, preferably, although otherratios can-be employed. Although, as explainedV below, asmall amount of diluent is produced in situ in the process, there is not a sufficient amount produced to-achieve the effect of this invention in a practical sense-and therefore the diluent in the above ratios refers to diluent from an external source. It is only when the diluentcomes from an external source that there is any control over the amount thereof in the system for purposes ofcontrol-of the reaction rate and reaction temperature. It -is explained below that the diluent of this invention servesa veryximportant purpose in regulation of thereaction rate and reaction temperature when the quantity thereof. introduced into the system can be regulated.

Suitablehydrocarbon diluent materials include single compounds orA mixtures of compounds such as saturated compounds including paraffins and naphthenes and unsaturated-materials such as aliphatic and cyclic monoolens and aromatics with ko'r`without small amounts of impurities such as sulfur, nitrogen and oxygen. It is preferred to employ mixtures of hydrocarbons, such as straight run petroleum fractions or hydrogenated petroleum fractions. In general, the diluent has a boiling range extending onf-the low side from 300 F., 350 F. or 400 F., depending on the highest temperature in the reactor, to as high as 750 F. or 850 F., or higher. The diluent .is substantially inert but some reactivity is not harmful. For example, it might undergo saturation or d esulfurizativon withouti adverse effect upon the process.

An additional and unexpected advantage of the present invention arises evidently from the fact that the diluent of this present invention imparts a strong condensation or liquefaction effect upon to the entire system. Since the amount of total liquid in the system is greatly enhanced, more liquid is available to absorb heat via vaporization in an adiabatic reaction system. Therefore, the diluent of the present invention provides a highly liquid environment capable of absorbing a great amount of heat of vaporization and therefore having a high heat sink capacity, whereby superior temperature control is achieved, permitting greatly extended adiabatic cycle lengths. Extended cycle lengths permit operation with an aged catalyst which presents a selectivity advantage because when a noble metal catalyst becomes aged it becomes more highly selective towards hydrogenation of diolefins over monoolens.

The most suitable noble metal catalysts include palladium and platinum. Palladium is highly preferred because it is less sensitive to sulfur contamination than platinum or nickel. A nickel catalyst bed, upon reacting with sulfur in the aromatic distillate or diluent streams, tends to become a rigid mass whereas this effect is not observed in the case of palladium. The catalyst can be supported upon alumina or any other conventional inert supporting material. A promotor, such as chromium, can be incorporated into the noble metal catalyst. The catalyst and conditions in the noble metal reactor are conventional and can include inlet temperatures as low as room temperature, or F., and outlet temperatures from 250 to 350, 375 or 400 F. The pressure can be above 800 or 1000 p.s.i.g. Suitable liquid hourly space velocities are between 0.5 to 10 or between 2.5 and 4. The hydrogen rate can be between 900 and 1500 or between 1000 and 1200 s.c.f. per barrel of aromatic distillate. The hydrogen can be at least about 60 or 80 percent pure.

The advantage of the low temperature reactor is that diolefins, which are the prime gumor polymer-forming olefins in the feed, and which are the olefins which are most easily hydrogenated, are hydrogenated at a temperature which is sufficiently low to prevent substantial polymerization. Substantially all the diolefins are hy-v drogenated at the low temperature, or at least enough so that the problem of gum-formation disappears. No significant monoolen hydrogenation need occur in the noble metal reactor. Once the gum-forming diolefins are selectively hydrogenated to monoolens without substantial hydrogenation of monoolens the aromatic distillate and diluent can then be relatively safely increased in temperature in a second reactor to hydrogenate the monoolens with a less valuable catalyst. The reason a noble metal is employed in the rst reactor is that its hydrogenation activity is so great that hydrogenation of diolefins can proceed at a sufficiently low temperature that polymerization thereof is at a very low level. With the removal of the diolefinic entity, which is the prime polymer-forming entity, the aromatic distillate from the noble metal reactor can either be safely utilized for gasoline blending without further treatment or, if benzene production is desired, it can safely be subjected to further hydrogenation at a higher temperature, permitting use of a less valuable and less active catalyst, preserving the activity of the noble metal catalytic entity. Therefore, the pres-V ent invention is directed towards the-low temperature hydrogenation of an aromatics-containing stream containing diolefinic hydrocarbons admixed with monoolenic hydrocarbons. Such mixtures are recovered from the thermal cracking of ethane, propane and butane mixtures and of naphtha to produce ethylene.

The second stage catalyst andhydrogenation reaction conditions are also conventional and include use of a catalyst containing at least one metal from Group VI and Group VIII. Examples include NiCoMo, CoMo, NiMo, and other conventional combinations, on an inert support, such as alumina. Temperatures are generally higher than in' the first reactor and can range from 300, 400 orv 500 F. up to 650 F., or higher, but temperatures should not be high enough to saturate aromatics. Suitable hydrogen partial pressures are 200 to 1200 p.s.i.g. Space velocities of 0.5 to 10, generally, and 1 to 4, preferably, liquid volumes of charge per volume of catalyst per hour can be employed. The hydrogen recycle rate can be between 1500 and 10,000 s.c.f. per barrel of aromatic distillate, or more, with preferred amounts between 3000 and 7000 s.c.f. per barrel. Hydrogen purity can range between 30 or 50 percent and 100- percent.

The process of the present invention is further illustrated by reference to the process flow diagram of FIG. 2 which illustrates a system comprising low and high temperature hydrogenation reactors in series. Aromatic distillate, obtained as a by-product from the high temperature (1500 F.) cracking of ethane, propane, butane and naphtha to produce ethylene is charged through line 12 to reactor containing a catalyst comprising palladium-chromium on alumina. The lowest inlet temperature of reactor -10 is 75 F. and the highest outlet temperature is 350 F. `Make-up hydrogen is added through line 14 and feed furnace oil -diluent is added through line 16.

The furnace oil has a boiling range of about 400 to 650 F. For every 1 volume of essentially saturated feed in the furnace oil boiling range charged to reactor 10 through line 18, about 1.02 volumes of hydrocarbon in the furnace oil boiling range is removed from reactor 10 through line which means that for every 1 volume of furnace oil charged, 0.02 part, or 2 percent, of unsaturated dimer and trimer material boiling in the furnace oil range is produced in reactor 10. These dimers and trimers are olefinic and become saturated under the higher temperature conditions in reactor 22. It is much safer to hydrogenate these dimers and trimers in reactor 22 because under the higher temperature conditions therein they are much more likely to become vaporized, in which state they cannot easily further polymerize to a solid material. In contrast, under the 10W temperature conditions in reactor 10 these materials are in the liquid state and in the liquid state can relatively easily polymerize to solid polymers and thereby deactivate the valuable palladium catalyst.

It is seen that for each 1 volume of saturated furnace oil boiling range material fed to reactor 10, 1.02 volumes of saturated furnace oil boiling-range material is available in the next pass. Therefore, the present process is self-generating in furnace oil diluent, or, stated otherwise, furnace oil boiling range hydrocarbon can be a by-product of the present invention. However, it is emphasized that in practical operation there will not be suicient furnace oil produced within the process to effectively achieve the advantage of the present invention and in order to achieve control over the total amount of liquid within the system with any reliability the diluent must be introduced or derived from an external source.

The low temperature conditions in reactor 10 are selective to hydrogenation of diolens, reserving hydrogenation of monoolens for the more severe conditions of reactor 22. Since the diolens are Igumor polymer-formers, their removal results in a product rich in monoolefins and aromatics which constitute high octane gasoline blending agents which can be removed from the process for said purpose through line 24. However, if it is desired to saturate the monoolens present to prepare a petrochemical product rich in benzene, toluene and xylene the efuent of reactor 10 is charged to reactor 22 containing NiCoMo on alumina catalyst through line 26 and preheater 28. A limited amount of heat is added at preheater 28 because hot furnace oil carries a considerable amount of heat from reactor 10 to reactor 22. Reactor 22 is operated within a temperature range of 375 to 650 F. at which temperature much of the furnace oil and aromatic distillate becomes vaporized, although some of the furnace oil remains in the liquid state. Efuent is removed from reactor 22 through line 30, from which furnace oil and hydrogen are separated and recycled through line 32 while petrochemical or gasoline product containing benzene, toluene, xylene and C9 and C10 aromatics is removed from the process through line 34.

The hydrocarbon diluent of the present invention has a boiling range above the boiling range of the aromatic distillate feed and thereby considerably increases the temperature at which total vaporization of the system occurs. For example, an aromatic distillate which completely vaporizes at 350 F. in a hydrogenation reactor is found to vaporize entirely at about 600 F. in the presence of 0.25 mole of 400-650 F. furnace oil per mole of, aromatic distillate and is found to vaporize entirely at about 650 F. in the presence of 0.5 mole of furnace oil per mole of aromatic distillate. Since a hydrogenation reactor is not operable without at least about 10 percent of the liquid feed being in the liquid phase, it is seen that use of a furnace oil can extend the maximum temperature in the noble metal reactor to more than 450 F., thereby extending the length of the run. The diluent of the presentV invention can result in 30 to 50 or 75 to 85 percent or more of the total liquid feed, including both diluent and aromatic feed, remaining in the liquid phase in the reactor.

Since the furnace oil or other diluent of this invention has a magnified eEect upon the amount of liquid present in the noble metal reactor, the reaction rate in said reactor can be controlled in part by adjusting the amount of diluent introduced from an external source. At the end of a catalyst cycle when reactor temperatures are relatively elevated, further elevation of reactor temperature can be diminished by reducing the ratio of diluent to aromatic distillate and thereby reducing the amount of liquid in the system. Since the liquid in the system tendsto mask the surface of the catalyst from not only aromatic distillate, but especially from hydrogen, a reduction of'the amount of liquid, will make it easier for reactants, and particularly for hydrogen, to reach the surface ofthe catalyst to improve the reaction rate as an alternative to an increase in temperature. This type of regulation as-l sumes that the quantity of liquid in the reactor is more than ample to inhibit solid polymer formation and provide the required heat sink. By the same token, an increase in the ratio of diluent to aromatic distillate would decrease the rate of reaction, if such were desired.

We claim:

1. A process for the hydrogenation of an aromatic distillate feed boiling in the gasoline range containing both diolens and monoolefinscomprising passing said aromatic distillate and hydrogen over a catalyst selected from the group consisting of platinum and palladium in a first reactor at a process temperature suciently low that that the hydrogenation reaction is selective to diolens over monoolens, charging a hydrocarbon diluent lwhose boiling range extends above the gasoline boiling range and which is a liquid under the reaction conditions and which increases the proportion of said feed in the liquid phase at said process temperature, charging the eluent including said diluent to a second hydrogenation reactor operated at a relatively higher temperatureand containing as a catalyst at least one metal selected from Groupy VI and Group VIII for the hydrogenation'ofsaid monoolens, and recycling said diluent from said second reactor to said rst reactor. y .-,v .A

2. The process of claim 1 wherein the temperatue in said iirst reactor is to 350 F. and the temperaturein said second reactor is 375 to 650 F.

3. The process of claim 1 wherein said diluent is introduced in a molar ratio of 0.1 to 2 with respect to said feed.

4. The process of claim 1 wherein said palladium.

S. In a process for the hydrogenation of an aromaticscontaining feed boiling in the gasoline range containing both diolelins and monoolens in a reactor containing a catalyst selected from the group consisting of platinum catalyst is and palladium at a process temperature sufficiently low that the hydrogenation reaction is selective to diolens over monooleins and said feed is at least partially in the liquid state, the improvement comprising charging to said process a furnace oil diluent defined by a 400 to 650 F. boiling range which is introduced to said process in a 0.1 to 2 molar ratio with respect to said aromatcs-containing feed, said diluent is a liquid under the reaction conditions and increases the proportion of said feed in the liquid phase at said process temperature.

6. In a process for the hydrogenation of an aromaticscontaining feed boiling in the gasoline range containing both diolens and monoolefins in a reactor containing a catalyst selected from the group consisting of platinum and palladium at a process temperature suiciently low that the hydrogenation reaction is selective to diolefins over monoolelins and said feed is at least partially in the liquid state, the improvement comprising charging to said process a hydrocarbon diluent having a boiling range defined by 650 F. to 850 F. Which is a liquid under the reaction conditions and which increases the proportion of said feed in the liquid phase at said process temperature.

7. In a process for the hydrogenation of an aromaticscontaining feed boiling in the gasoline range containing both diolefns and monoolens in a rst reactor containing a catalyst selected from the group consisting of platinum and palladium at a process temperature sufficiently low that the hydrogenation reaction is selective to diolens over monoolefins and said feed is at least partially in the liquid state, the improvement comprising charging to said process a hydrocarbon diluent whose boiling range extends above the gasoline boiling range which is a liquid under the reaction conditions and which increases the proportion of said feed in the liquid phase at said process temperature, charging the efliuent including diluent of said first reactor to a second hydrogenation reactor operated at a relatively higher temperature and containing as a catalyst at least one metal selected from Group VI and Group VIII for the hydrogenation of saidI monoolefins, and recycling said diluent from said second reactor to said first reactor.

8. In a process for the hydrogenation of an aromaticscontaining feed boiling in the gasoline range containing both diolefns and monoolefins in the presence of a catalyst selected from the group consisting of platinum and palladium at a process temperature sufficiently low that the hydrogenation reaction is selective to diolens over monoolelins and said feed is at least partially in the liquid state, the improvement comprising charging to said process a furnace oil diluent Whose boiling range extends above the gasoline boiling range in at least a 0.1 mole ratio with respect to said feed and which is a liquid under the reaction conditions and which increases the quantity of said feed in the liquid phase at said process temperature, operating said process under substantially adiabatic conditions, and said increased quantity of liquid absorbing heat of reaction by vaporization to extend the cycle life of said process.

9. In a process for the hydrogenation of an aromaticscontaining feed boiling in the gasoline range containing both diolefins and monoolefins in a rst reactor in the presence of a catalyst selected from the group consisting of platinum and palladium at a process temperature from r to 375 F. to selectively hydrogenate diolefns over monoolens sothat said feed it at least partially in the liquid state, the improvement comprising performing said process in the presence of a furnace oil range hydrocarbon diluent present in at least a 0.1 molar ratio with respect to said feed which is a liquid under the reaction conditions and which increases the quantity of said feed in the liquid phase at said process temperature, operating said process under substantially adiabatic conditions, said increased quantity of liquid absorbing heat of reaction by vaporization to extend the cycle life of said process, charging the eflluent of said first reactor including said diluent to a second hydrogenation reactor operated at 400 to 650 F. and containing as a catalyst metal selected from Group VI and Group VIII for hydrogenating said monoolens, and recycling said diluent from said second reactor to said iirst reactor.

References Cited UNITED STATES PATENTS 3,075,917 l/l963 Kronig et al. 20S-144 3,167,498 1/1965 Kronig et al 208-143 3,215,618 1l/l965 Watkins 208-l43 3,221,078 11/1965 Keith et al. 20S-143 3,309,421 3/1967 Kirk et al. 208-143 3,451,922 6/ 1969 Parker 208-143 3,493,492 2/ 1970 Sze 20S-143 3,496,095 2/ 1970 Lewis 20S-143 3,537,982 ll/l970 Parker 20S-143 HERBERT LEVINE, Primary Examiner U.S. Cl. X.R.

ggsg@ UNHED STATES PATENT @Friet CERTIMCATE 0F CRRECEION Patent N0. 3,654,132 Dated April 4, 1972 Inventor(s) Robert D. Christman and Joel D. McKinney It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line l2, delete "actors utilizing a noble metal catalyst are conventionally" and substitute therefore activity is sufficiently high to permit reaction at a relatively-- ySigned and sealed this lst day of August 4lf'.

(SEAL) Attest:

EDWARDMQFLETCHEJRJRQ ROBERT GOTTSCHALK Attesting Officer' Commissioner' of Patents 

